The present invention relates to a method for making silicone-polycarbonate block co-polymers. In particular, the invention relates to a method whereby polycarbonate oligomers having terminal hydroxy groups are produced by a melt reaction of polycarbonate resin with a dihydric phenol in the presence of a catalyst and in the absence of an organic solvent. The oligomers are thereafter combined with polyorganosiloxanes having terminal chloro-organo siloxy groups to produce the block co-polymers. The method employed is effective to produce the block co-polymers without directly using phosgene gas in the final synthesis.
A siloxane polycarbonate resin can be made in a two-step process involving first reacting chloro end group siloxane oligomers with an excess of bisphenol-A (BPA), then reacting the resulting phenolic hydroxy end group siloxane with additional BPA and phosgene in a conventional interfacial phosgenation reaction to yield the desired block co-polymer. One such useful polycarbonate-polydimethylsiloxane block co-polymer contains 43 weight percent siloxane units with an average block length of about 10. The material has utility as an impact modifier in blends with polycarbonate resin and as a film used as an interlayer in multilayer laminates of polycarbonate resin sheets and acrylic resin sheets. Typically, these laminates consist of two or more layers of polycarbonate sheet, optionally with an internal layer of acrylic sheet, with the resin interlayers serving as an adhesive and as a spacer to separate the sheets.
In a particular process set forth in Vaughn, U.S. Pat. No. 3,189,662, assigned to the Assignee herein and incorporated herein by reference, silicone-polycarbonate block co-polymers are made by phosgenating a mixture of dihydric phenol terminated polydiorganosiloxane and dihydric phenol in the presence of an organic solvent and an acid acceptor. Although the method results in the production of silicone-polycarbonate block copolymers useful in a variety of applications, such as injection moldable thermoplastics and elastomers having improved tensile properties, the method requires the direct use of phosgene gas in the final synthesis.
Silicone-poly(arylcarbonate) block co-polymers can be made without directly using phosgene gas in the final synthesis of the block co-polymer as set forth in Evans, U.S. Pat. No. 4,920,183, assigned to the Assignee herein. A hydroxyaryl terminated poly(arylcarbonate) oligomer having an average of about 2 to about 1,000 chemically combined arylcarbonate units is interconnected with a chlorine terminated polydiorganosiloxane having an average of about 2 to about 1,000 chemically combined diorganosiloxy units, in the presence of an organic solvent and an acid acceptor. The silicone-poly(arylcarbonate) block co-polymer is recovered from the mixture for example by addition of the reaction mixture to a precipitating solvent such as methanol.
Evans et al. '183, also discusses the manufacture of hydroxyaryl oligomers. According to Evans et al., these oligomers can be made by effecting the polymerization of cyclic arylcarbonates in the presence of phenol or bisphenol-A (BPA) as shown in U.S. Pat. No. 4,849,502, assigned to the Assignee herein and incorporated by reference.
Evans et al. discusses another procedure which can be used to make hydroxyaryl oligomers by the controlled reaction in a suitable solvent of high molecular weight polycarbonate resin with a phenol or polyhydric phenol and a polymerization initiator, such as alkaline metal phenoxide or polycarbonate formation catalysts as set forth in Brunelle et al., U.S. Pat. No. 4,644,053, assigned to the Assignee herein and incorporated by reference.
Chlorine terminated polydiorganosiloxane can be made by known procedures such as by the controlled hydrolysis of diorganodihalosilane, for example, dimethyldichlorosilane set forth in U.S. Pat. Nos. 2,381,366 and 2,629,726. Another procedure which can be employed to make chlorine terminated polydiorganosiloxane is the equilibration of a mixture of diorganochlorosilane and a cyclic polydiorganosiloxane, for example, octamethylcyclo-tetrasiloxane, in the presence of a metal catalyst such as ferric chloride as set forth in U.S. Pat. No. 2,421,653.
Japanese patent application no. 60-114576 discloses a process to produce low molecular weight polycarbonates having terminal hydroxy groups produced by the reaction of high molecular weight polycarbonates with hydroxy compounds, e.g. 1,6-hexane diol and diethylene glycol. Although 2,2-bis(4-hydroxyphenyl)propane is disclosed within a long list of possibly useful candidate hydroxy compounds, it is not mentioned as a preferred compound. No disclosure is made in the reference as to the ratio of bisphenol-A to polycarbonate. The reference also fails to disclose reacting a hydroxyaryl terminated polycarbonate oligomer with a polydiorganosiloxane to form a polycarbonate-polysiloxane block co-polymers. Industry is currently seeking simplified processes for producing silicone-polyarylcarbonate block co-polymers with reduced solvents and without the direct use of phosgene gas.